Posted March 9, 2021

Design Considerations for Small-Batch CNC Machining Online Quotes

A lathe processes a small-batch CNC machining online quote

Design engineers commonly design a product for efficient fabrication. This early consideration helps reduce time and expense during manufacturing, which is essential when ordering thousands of parts. For small-batch orders, companies often omit this step in favor of getting the project completed as quickly as possible.

Rushing the part through design may seem like a solution to save time on a small order, but there are many risks in this approach. The design may lack details, which could slow down its production or add costs during manufacturing. If the part is a prototype, a rushed design could result in expensive production costs and multiple redesigns before it transitions to mass-production. To avoid these problems, consider some design guidelines before submitting a small-batch CNC machining online quote for manufacturing.

Expense Considerations with Small-Batch CNC Machining Online Quotes

There are several reasons for ordering small batches of parts from a CNC machine shop. Sometimes a company needs a part quicker than offered by an offshore facility. In other cases, they need a limited run of parts for prototyping a new design, or the customer is cutting back on expenses. Whatever the reasons, one should consider specific details that could affect the bottom line when planning a small-batch CNC machining online quote. 

A machine shop establishes a setup price for preparing any production order. The data requires analysis and programming into machines. Next, operators prepare for their work and set up the project with the appropriate fixtures and tools. These costs spread out among the units in the order. There's typically a steep per-unit price drop from one to two parts, and even in prototyping most manufacturers typically order five units.The smaller the order, the greater the setup cost per unit. Additionally, ordering materials for smaller orders requires greater per-unit investment than ordering the materials in bulk.

Another expense consideration for smaller orders relates to how the machine shop processes the order. The larger the order, the more the shop can look at ways to increase its production efficiency. For instance, a machine shop can use a tombstone fixture to manufacture several units of the same  part simultaneously on one mill. Turned parts can leverage a bar feeder for producing multiple units quickly. One method to increase efficiency involves running larger orders across multiple machines. However, these methods aren’t cost-effective on smaller orders, which manufacture as “one-offs,” increasing their per-unit costs. 

Design Guidelines to Consider for a Small-Batch Order

There are some design tactics to keep in mind to make a part more manufacturable:

  • Internal corners: The sharper the internal corners in a part, the smaller the tools. Smaller tools mean more milling passes to remove material, which increases time and expense. Design parts that machinists can mill with larger tools to speed up the machining process. One can achieve this by specifying larger fillets instead of sharp internal corners.

  • Cavity depth: CNC cutting tools cannot reach internal surfaces beyond a certain depth. To avoid creating a design that can’t be machined, limit the depth of internal cavities to four times the tool width.

  • Feature alignment: The shape and contours of the part will determine the machining and how much setup it will require. The more complex the part, the more expensive the manufacturing. Simplifying the design will reduce the amount of repositioning necessary during machining. Not only does repositioning the part add manufacturing time and expense, but it can also introduce positional errors.

  • Don’t over-tolerance the design: Parts with specified tolerances cost more to produce than those that rely on a default tolerance. In some cases, these additional tolerances are selected out of repetition and not because the design itself requires them. If your design doesn’t need special tolerances, don’t use them.

  • Materials and surface finish: Material costs are more volatile now than ever. The materials you select may not only lower your overall production costs, but they may speed up the production time (depending on their availability). Surface finishes also add cost, so if your part doesn't require a unique finish, don’t request it.

  • Drawings: Including a manufacturing drawing with your CAD model will help speed up the setup time by specifying threads, specific tolerances, surface finishes, or other notes and instructions.

Keep in mind that ultimately the needs of the part dictate the design. These guidelines simply show how to save time and expense if the part design allows for it. The best option is to collaborate with the CNC machine shop to design the most cost-effective part for small-batch orders.

How Your CNC Machine Shop Can Help with Your Order

Many experienced CNC machine shops can help with your small-batch order through their online quotation and part evaluation system. An online quote tool allows you to upload your CAD model for an automated design review, and if machinable, you will get an immediate quote. If not, you will have the option to change the order’s parameters, change the CAD model, or contact the shop for additional support.

An established CNC machine shop works with orders from various customers, and they will answer your questions about design, materials, and surface finishes. First, they will determine your business goals to make the best recommendations based on your needs. If you require a part built quickly, their suggestions will differ from designs focused on final production quality. For designs that need to cut costs, the machine shop will provide a different set of recommendations concerning material selections and finishes. No matter which route you take, the machine shop will help you make the best decisions and choices to get your design processed quickly and at the highest quality.

At Plethora, we specialize in manufacturing precision parts using the industry's most advanced CNC machining equipment and software. Our sales team includes engineers who understand the technical choices necessary for building a design according to your specifications. Our primary goal is to ensure we manufacture your part to the highest quality. Our online DFM and quoting systems are ready to receive your data so we can begin working with you on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.

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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, Design, Manufacturing, finishing, CNC machining, Quality, Prototyping, Small Batch